Age hardening cobalt base alloy



United Sttes 1 3,047,382 AGE HARDENING COBALT BASE ALLOY Norman R. Harpster, Canonsburg, Pa., assignor to Universal-Cyclops Steel Corporation, Bridgeville, Pa., a

corporation of Pennsylvania No Drawing. Filed Jan. 13, 1959, Ser. No. 786,463

8 Claims. (Cl. 75-171) This invention relates to cobalt base alloys that combine the desirable characteristics of being age hardenable by heat treatment to high hardness and tensile properties and having good stress-rupture strength.

There are commercially available cobalt base alloys that evidence strength maintained at high temperature. Conventionally such alloys are strengthened by the additions of elements such, for example, as tungsten, molybdenum and columbium. To render such alloys responsive to heat treatment so that the best characteristics of strength, tensile properties and hardness are obtained, alloying additions of titanium and aluminum have been used.

It is therefore apparent that the desirable properties in such cobalt base alloys are achieved in a way that is of considerable significance from an economic point of view. The base alloy itself is costly and the addition of expensive alloying constituents further increases the expense involved.

It is an object of the present invention to provide new and useful cobalt base alloys that can be age hardened by heat treatment to high hardness and tensile properties, and have good stress-rupture strength.

It is another object of this invention to provide alloys in accordance with the foregoing object without need to use highly expensive alloying additions.

The invention is predicated upon my discovery that its stated objects are attained with cobalt base alloys containing, by weight, at least 0.10 percent of carbon and the remainder cobalt to which is added at least an amount.

of phosphorus that is effective to characterize the resulting products with age hardenability. A composition range for alloys of my invention within the foregoing broad range is, by weight, 12 to 30 percent of chromium, 10 to 30 percent of nickel, at least 0.10 percent of carbon, up to 20 percent of iron, at least 0.08 percent of phosphorus and the remainder cobalt. In addition, incidental impurities and alloying elements that do not deleteriously afiect the desired characteristics of the resulting alloy may be present. For example, additions of molybdenum, tungsten or both may be made in amounts of about 0.5 to percent where it is desirable to further enhance elevated temperature strength and the cost of such additions is not prohibitive, considering the desired result.

Within the foregoing limits, I now prefer that the phosphorus-containing cobalt base alloys of my invention contain, by weight, about 0.15 to 1.00 percent of carbon, 0.08 to 0.40 percent of phosphorus, 12 to 30 percent of chromium, to 30 percent of nickel, 0 to 20 percent of iron and the remainder cobalt along with incidental impurities and alloying elements as above described, if desired.

A typical composition range within which the maximum benefits of my invention would be attained is 0.15 to 0.75 percent of carbon, 0.15 to 0.40 percent of phosphorus, 12 to 25 percent of chromium, 10 to 25 percent of nickel, 0 to 15 percent of iron and the remainder cobalt along with incidental impurities and alloying elements as previously described, when desired.

" 3,047,382 EC Patented July 31, 1962 2 Cobalt base alloys of the foregoing composition may be made according to normal procedure for high strength alloys. For example, the alloys may be air or vacuum melted, or melted in a controlled atmosphere, and cast into ingots. These ingots may be wrought by usual mill practices into forgings, bars, sheet, strips, or other forms. The resulting products may then be used for producing various useful articles that are now prepared from highstrength cobalt alloys. Either the bar or finished article may be solution heat treated and aged to the desired degree of hardness.

The excellent properties of the alloys of my invention and the high degree of response to heat treatment in addition to the characteristically good tensile properties and good stress-rupture strength are exemplified by alloys prepared with a melting aim, by weight, of 0.25 to 0.30

' percent of carbon, percent of chromium, 20 percent of nickel, varying percentages of phosphorus and the balance cobalt. Four heats were prepared so that they would have the same basic composition except for a variation in the phosphorus content; The analyses of the four heats were as follows:

Table 1 Heat 0 P Or Ni Co 0 25 0.003 19. 54 18.90 Balance. 0 21 0. 081 19. 54 18.90 Do. 0. 30 0.100 19. 72 19. 40 Do. 0. 31 0. 240 19. 72 19. 40 Do.

All four ingots were forged into bars from which specimens were obtained to determine the response to aging, stress-rupture characteristics and tensile properties at room and elevated temperatures.

The aging data on these four heats, shown in Table III, Where obtained at aging temperatures ranging vfrom 1100 to 1600 F. after solution treating at temperatures from 1900 to 2200 F. and water quenching. These data were developed on standardized tests with respect to time at both solution and aging temperatures. In addition to the data on heats A, B, C and D, data on four other heats are included in Table III. The analysis of each additional heat was:

The hardness data together with the heat treatment used on all of the foregoing heats were as follows:

of phosphorus and the remainder cobalt together with incidental impurities and elements that do not deleteriously affect the characteristics of the resulting alloy.

3. A cobalt base alloy in accordance with claim 2, said carbon content being in the range of 0.15 to 1.00 percent.

'4. An alloy in accordance with claim 3 containing about 0.5 to 5 percent of at least one element selected from the group consisting of molybdenum and tungsten.

5. An age hardenable cobalt base alloy consisting essentially of, by weight, 0.15 to 0.75 percent of carbon, 0.15 to 0.40 percent of phosphorus, 12 to 25 percent of chromium, 10 to 25 percent of nickel, up to 15 percent of iron and the remainder cobalt together with incidental impurities and elements that do not deleteriously affect the desired characteristics of the resulting alloy.

6. An age-hardenable cobalt base alloy consisting essentially, by weight, of 0.15 to 1.00 percent of carbon, 0.08 to 0.40 percent of phosphorus, 12 to 30 percent of chromium, 10 to 30 percent of nickel and the remainder cobalt together with incidental impurities and elements that do not deleteriously affect the desired characteristics of the resulting alloy.

7. An alloy in accordance with claim 6 containing about 0.5 to 5 percent of at least one element selected from the group consisting of molybdenum and tungsten.

8. An age-hardenable cobalt base alloy consisting essentially, by weight, of 0.15 to 0.75 percent of carbon, 0.15 to 0.40 percent of phosphorus, 12 to 25 percent of chromium, 10 to 25 percent of nickel and the remainder cobalt together with incidental impurities and elements that do not deleteriously afiect the desired characteristics of the resulting allov.

References Cited in the file of this patent UNITED STATES PATENTS 2,200,742 Hardy May 14, 1940 2,513,303 Feild July 4, 1950 2,643,221 Brenner et al June 23, 1953 OTHER REFERENCES Haynes Alloys, 1950, pages 26, 27, 32, 33, 84 and 20 85. Published by Union Carbide Corp, New York, NY.

Hansen: Constitution of Binary Alloys, 1958, pages 488-489. Published by McGraw-Hill Book 00., Inc., New York, NY. 

2. AN AGE HARDENABLE COBALT BASE ALLOY CONSISTING ESSENTIALLY OF, BY WEIGHT ABOUT 12 TO 30 PERCENT OF CHROMIUM, 10 TO 30 PERCENT OF NICKEL, AT LEAST 0.10 PERCENT OF CARBON. UP TO 20 PERCENT OF IRON. 0.05 TO 0.40 PERCENT OF PHOSPHORUS AND THE REMAINDER COBALT TOGETHER WITH INCIDENTAL IMPURITIES AND ELEMENTS THAT DO NOT DELETERIOUSLY AFFECT THE CHARACTERISTICS OF THE RESULTING ALLOY. 